In this study, we demonstrate a polarization imaging camera with a waveplate array of a silica glass fabricated by femtosecond (fs) laser direct writing. To use a waveplate array of silica glass for polarization imaging, non-uniformity of the transmittance and retardance in the waveplates must be considered. Therefore, we used a general method of polarization analysis with system matrices determined experimentally for all the units in the waveplate array. We found that a figure of merit based on the determinant of the system matrix could be applied to improve the accuracy of analysis and the robustness to the retardance dispersion for both the simulated and the fabricated waveplate array.

Birefringent optical elements can be fabricated by inscribing structures of nanogratings inside a silica glass by focusing femtosecond (fs) laser pulses. When birefringent optical elements are used as phase retarders, the retardance of the birefringence and transmittance are important properties to determine the quality as a phase retarder. Our target of application of fs-laser-induced birefringent structures inside a silica glass is a polarization imaging filter, which can capture the polarization distribution of detected light in a real-time. Larger retardance and higher transmittance of a filter are required to acquire polarization with higher accuracy and sensitivity. Therefore, it is necessary to elucidate the relationship between laser processing conditions and the induced birefringent structures. In this study, the authors have investigated fs-laser induced birefringent structures under various processing conditions. The authors have confirmed that the retardance and transmittance of the induced structures depend on the focusing depth from the glass surface. The authors also demonstrate that spherical aberration due to a refractive mismatch between the air and glass can be changed by modulating the spatial phase distribution of fs laser pulses with a spatial light modulator (SLM) and birefringent structures with larger birefringence could be fabricated at a desired depth inside a silica glass by using an SLM.

Using a pulsed 193-nm 10-Hz ArF excimer laser with the amplitude mask technique, we report a comparative study of sensing capabilities (refractive index and chemical solution) for three different long-period grating configurations written in a Furukawa single mode fiber. The three gratings investigated in this work were a typical long-period grating, a phase-shifted long-period grating, and a long-period grating written in a biconical tapered fiber. The principle of operation is based on the measurement of resonant wavelength shift through the change of refractive index of medium surrounding the cladding surface of the gratings. Previous studies of the three different gratings were conducted by using different fabrication methods (point-to-point writing), irradiation sources (electric-arc discharges, frequency doubled argon ion laser, and CO2 laser) and fiber types. The amplitude mask technique with a 193-nm ArF excimer laser has successfully been produced the three different long-period grating configurations and yielded comparable sensing performance with high sensitivity. Experimental results demonstrated that these fiber grating sensors could provide a resolution of ~10 -3 to 10 -4 for refractive indices in the range of 1.34 to 1.41, suggesting that these sensors are attractive for chemical sensing and RI measurements with aqueous solutions.

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